1. Field of the Invention
The present invention relates to an in-vehicle wireless terminal mounted to a vehicle and having a function to perform wireless communication with a wireless base station.
2. Description of Related Art
An in-vehicle wireless terminal mounted to a vehicle can be configured to control transmission power. For example, the in-vehicle wireless terminal increases the transmission power if the in-vehicle wireless terminal cannot perform the wireless communication with the wireless base station, e.g., if an antenna is disconnected or if an antenna wire (i.e., a connecting wire which connects the antenna to the in-vehicle wireless terminal) is disconnected. Because of the above configuration, if the in vehicle wireless terminal cannot perform the wireless communication with the wireless base station, the in-vehicle wireless terminal seeks to recover or establish the wireless communication with the wireless base station. It should be noted that the above-described situation where the in-vehicle wireless terminal cannot perform the wireless communication with the wireless base station includes a situation where the in-vehicle wireless terminal cannot establish a communication link. Thus, a disconnection of the antenna or the antenna wire is not a complete disconnection that completely disables wireless communications capacity. A disconnection of the antenna or the antenna wire includes a disconnection that does not completely disable the wireless communications capacity of the in-vehicle wireless terminal but decreases the wireless communications capacity of the in-vehicle wireless terminal.
Since a vehicle travels, the vehicle may travel so as to approach the wireless base station, may travel so as to recede from the wireless base station, or may keep traveling in places faraway from, the wireless base station. Thus, if the vehicle keeps traveling while receding from the wireless base station for a long time period or keeps traveling in places faraway from the wireless base station for a long time period, the transmission power is maintained at a high level for the long time period. This can causes a problem of wasted power consumption, heating the in-vehicle wireless terminal, or the like. JP-2003-298507A (corresponding to Japanese Patent No. 3846351) describes a mobile wireless terminal that suppresses power consumption by prohibiting data transmission if the mobile wireless terminal is inside a structural body causing a weak electric filed such as a tunnel and the like.